In 1989, a main causative virus of non-A non-B post-transfusion hepatitis was found and named hepatitis C virus (HCV). Since then, several types of hepatitis viruses have been found besides type A, type B and type C, wherein hepatitis caused by HCV is called hepatitis C. Subjects infected with HCV are considered to involve several percent of the world population, and infection with HCV characteristically becomes chronic.
HCV is an envelope RNA virus, wherein the genome is a single strand plus-strand RNA, and belongs to the genus Hepacivirus of Flavivirus (from The International Committee on Taxonomy of Viruses, International Union of Microbiological Societies). Of the same hepatitis viruses, for example, hepatitis B virus (HBV), which is a DNA virus, is eliminated by the immune system, and infection with this virus ends in an acute infection except for neonates and infants having yet immature immunological competence. In contrast, HCV somehow avoids the immune system of the host due to an unknown mechanism. Once infected with this virus, even an adult having a mature immune system frequently develops persistent infection.
When chronic hepatitis is associated with the persistent infection with HCV, it advances to cirrhosis or hepatic cancer in a high rate. Enucleation of tumor by operation does not help much, because the subject often develops recurrent hepatic cancer due to the sequela inflammation in non-cancerous parts.
Thus, an effective therapeutic method for treating hepatitis C infection is desired. Apart from the symptomatic therapy to suppress inflammation with an anti-inflammatory agent, the development of a therapeutic agent that reduces HCV to a low level free from inflammation and that eradicates HCV has been strongly demanded. An optimal therapeutic agent would provide a virologic response classified as a “sustained virologic response,” which is defined as undetectable levels of virus in blood six months or more after completing hepatitis C therapy.
At present, treatments with interferon, as a single agent or in combination with ribavirin, are the only effective method known for the eradication of HCV. However, interferon can eradicate the virus only in about 33–46% of the subject population. For the rest of the subjects, it has no effect or provides only a temporary effect. Therefore, an anti-HCV drug to be used in the place of or concurrently with interferon is awaited in great expectation.
Cyclosporin A is well known for its immunosuppressive activity and a range of therapeutic uses, including antifungal, anti-parasitic, and anti-inflammatory as well as anti-HIV activity. Cyclosporin A and certain derivatives have been reported as having anti-HCV activity, see Watashi et al., 2003, Hepatology 38:1282–1288, Nakagawa et al., 2004, Biochem. Biophys. Res. Commun. 313:42–7, and Shimotohno and Watashi, 2004, American Transplant Congress, Abstract No. 648 (American Journal of Transplantation, 2004, 4(s8): 1–653).
However, a problem with known cyclosporins is their nephrotoxicity. For example, cyclosporin A (cyclosporine) can cause nephrotoxicity and hepatotoxicity. Nephrotoxicity, a serious complication of cyclosporine therapy, is characterized by intense renal vasoconstriction that often progresses to chronic injury with irreversible structural renal damage (Busauschina et al., 2004; Myers et al., 1988). Nephrotoxicity associated with cyclosporine has been noted in 25 to 38% of transplant subjects. Renal dysfunction can occur at any time and ranges from an early reversible damage to a late progression to irreversible chronic renal failure. Acute nephrotoxicity may appear soon after transplantation or after weeks or months, with oliguria, acute decrement of glomerular filtration rate and renal plasma flow (Kahan, 1989).
In prolonged cyclosporine administration, chronic nephrotoxicity is characterized by a progressive and mostly irreversible impairment of renal function, and it is supported by histological lesions ranging from striped fibrosis to ischemic collapse of the tuft, glomerular sclerosis and tubular atrophy.
Effective methods and compositions for the treatment or prevention of hepatitis C infection are needed to combat the virus worldwide.